The Sturgeon Blue Moon will occur on August 21-22, 2021! What is a Blue Moon, exactly? Read all about Blue Moons.
Catch the Sturgeon Blue Moon
August’s full Moon, which is traditionally known as the Sturgeon Moon, is extra-special this year: it’s a seasonal Blue Moon!
Most of the time, a season (winter, spring, summer, or fall) contains three full Moons. However, if the dates of the full Moons and the seasons line up just right, a season may end up containing four full Moons instead. If that happens, the third full Moon of the season is called a seasonal Blue Moon! That’s exactly the case in August 2021.
When to See the Sturgeon Blue Moon
This full Moon will appear on the night of Saturday, August 21, before reaching peak “fullness” the next morning (when it will be hidden below the horizon). Venture outside just after sunset and keep an eye on it through the night to see it swim slowly across the sky!
→ Why is August’s Moon called the Sturgeon Moon? Learn all about it on our August Full Moon page!
What Is a Blue Moon?
Need a refresher on what a Blue Moon actually is? We get a lot of questions about the term, including:
- Is “Blue Moon” a scientific term used in astronomy?
- Did this term originate with Native American folklore, like a number of the other full Moon names?
- Does a Blue Moon really look blue?
In truth, the answer to all of these questions is “no.”
The modern understanding of “Blue Moon” only took off in the 1980s. It was a result of a much earlier mistake printed in a 1946 issue of Sky & Telescope magazine, and since then, the term has gone viral in the media.
Two Types of Blue Moons
There are two definitions of the term that are commonly used today:
- Seasonal Blue Moon: The extra full Moon that occurs within an astronomical season. One season—defined by the dates of the solstices and equinoxes—typically has three full moons occur within it. If a season instead has four full moons, then the third full moon (not the fourth) in the season may be called a Blue Moon.
- Calendrical Blue Moon: The second full moon to occur in a calendar month. It takes our Moon about 29.5 days to complete one cycle of phases (from new Moon to new Moon), so if a full Moon occurs on the first of a month, there will be a second full Moon—a Blue Moon—at the end of the month, too (except in February).
Although the latter definition is the one more commonly followed today, the former actually came first. As mentioned above, a misinterpretation of the seasonal definition in the 1940s gave way to the calendrical definition, which was later popularized in the 80s and has stuck around to today.
When Is the Next Blue Moon?
As of this writing, the next Blue Moon according to either definition will occur on August 22, 2021, as described in detail above.
After that, we’ll have to wait a couple of years for another Blue Moon:
- The next calendrical Blue Moon will happen on August 30, 2023, as the second full Moon in that month.
How Often Does a Blue Moon Occur?
Most months have one full Moon, not two.
Since the Moon’s period of phases is 29 ½ days, while months usually have 30 or 31 days, it’s obvious that if a full Moon lands on the first day of any month except February, it will repeat again at the end.
Turns out, calendrical Blue Moons happen every 30 months on average. Two and a half years. Seasonal Blue Moons happen at a similar rate: about once every two to three years. So maybe “once in a Blue Moon” isn’t so rare after all!
Two Blue Moons in a Single Year
But how often do we have two Blue Moons in a single year? (As in 2018, when there were Blue Moons in both January and March, and no full Moon in February.)
This won’t happen again until 2037, when we’ll again have another Blue Moon in both January and March.
Learn More
Want to learn more about the Moon? See the Almanac’s Moon Phase Calendar and Full Moon Calendar!
Reader Comments
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Once In A Blue Moon?
We should change the expression to "Once in a Super Blue Blood Moon"!!!
Blue Moon
Hey Bob,
I noticed that both January and March of 2018 have a "Blue Moon," and as a consequence, sandwiched in between is February with no full moon at all. It might be fun to calculate the odds of this occurrence and come up with a fun name for it. :)
Keep up the good work and Cheers! -Fred
Blue Moon
A Blue Moon is the forth full moon in a quarter,not the second in a month.
Blue Moon Definitons
Generally, both definitions are accepted.
Whenever the moon is low it
Whenever the moon is low it looks absolutely enormous. This is the famous "Moon Illusion." I think maybe we'll do a blog about it soon, right here!
Bob B
Last night me and my 5 year
Last night me and my 5 year old grandson went out to see the moon. He said it is so big about that time he grabbed me and said why is the mooonn moving it appeared to be jumping left and right also up and down what causes this?
See my comment, just above
See my comment, just above --
Bob
Last nights full moon did
Last nights full moon did apear here,East tuscaloosa Co. Al. a light blue.Around * pm CDT. Yellow afew min. later. I think This is a rare phenomonom that sarted the term. I believe I have read of this. I feel the origonal use was based on this and had mothing to do with calender days. Also we are wasting valuble sleep time debating this. Good night. Still would like other coment if others have acully seen a blue moon.
Event for August to be seen
Event for August to be seen through the telescope?
I took a excellent picture of
I took a excellent picture of the blue moon tonight. My grandchildren (the Twins)thought it was an actual blue moon, funny. Beautiful glow of brightness with the grayish crater to be seen. Can another event be seen in August through the telescope for the grand children?
I heard we won't see another
I heard we won't see another one til 2018.
The song 'Blue Moon' was
The song 'Blue Moon' was written in 1934 so the 1940's couldn't have been the source of the terminology.
I'm not sure that's what he's
I'm not sure that's what he's getting at. He's just saying that "Once in a Blue Moon" is now a common expression that means something rarely happens. But in the world of astronomy, a "Blue Moon" (the second full Moon in a month) is not really a rare event. It happens every 2 to 3 years. And it's also just a normal calendar thing since a moon cycle is about a day shorter than a calendar month.
I understood that the
I understood that the original calender was 13 months and when we went to a 12 month calender we had to have 2 moons in one month. But if it is every 2/1/2 years then that doesn't really make sense.
Maxine
I just read about the 19 year
I just read about the 19 year metonic moon cycle, that on July 31, 2015 there will be a blue moon, and every 19 years after that, this cycle will place a blue moon on July 31 (2034). But there was a blue moon on July 31, 2004- less than 19 years back. Was the 2004 blue moon special in some way that it was not part of this 19 year cycle? Can you please explain this to me?
is it true that if one
is it true that if one cuts his hair right after a full moon, his hair will grow back at a slower pace than if he cut it before the full moon?
Bob's column is about
Bob's column is about astronomy. That said, there is indeed an an age-old astrology belief that the Moon affects hair growth. You can find our best days to cut hair--to encourage growth or discourage growth--here on this timetable:
www.almanac.com/bestdays/timetable
I have another question for
I have another question for you:
In January of 2000 (I think it was a Wednesday, maybe the 26th of January), I was living in Washington DC area at that time on the top floor of an apartment building. I looked out my big living room window to the southwest facing night sky (10:00 ish). I saw a green light arch and hook and then it was gone. I think it was a comet. How can I find out more about it, or at least verify it?
My daughter was born "under"
My daughter was born "under" the Blue Moon on July 31, 2004. We looked it up in the Farmers Almanac and it said that Blue Moon of July 31, 2004 was called the Thunder Moon.
Now on July 31st, exactly 11 years later, there will be another July 31st Blue Moon. Will it also be the Thunder Moon, or will it have another name?
Yes, the full Moon on July 31
Yes, the full Moon on July 31 can be called a Thunder Moon. Actually, any full Moon around July can be named Thunder Moon, which was an Algonquin name, in addition to Buck Moon. The Colonial Americans also used the term Thunder Moon, as well as a few others. When two full Moons occur in one month, we list an alternate name for the second. Moons around the time of July were also known by names such as Raspberry Moon (Ojibway), Peaches Moon (Natchez), Crane Moon (Choctaw), and Moon when the Cherries are Ripe (Lakota Sioux).
Early Native American/First Nations tribes kept track of time by observing the seasons and lunar months. Learn more about full Moon names: www.almanac.com/content/full-moon-names
Hope this helps, and please extend our Happy Birthday wishes to your daughter!
When is the "Horns of the
When is the "Horns of the Moon" —which is supposed to be the best time to stop an addiction? A friend stopped a 4 pack a day smoking habit easily....no problem. Several months later an astrologist told him it was because he did it on the Horns of the Moon. I have wondered about this for years.
No idea about this folklore.
No idea about this folklore. But I hope they're successful in kicking that habit.
A true Blue Moon is the 3rd
A true Blue Moon is the 3rd of 4 Full Moons that fall between the seasonal markers. ~SHE
Actually, there is no true
Actually, there is no true blue moon that's accepted officially by anyone. Nowadays the most widely accepted definition is the second full moon in the same calendar month. Previously, and only in Maine, a local publication had defined it the way you just did.
What is the full story on
What is the full story on what we call a "Blue Moon"? Why call it "Blue"? The article mentions it came from a misunderstanding, it seems like there would be some other term applied. Maybe "Double Moon" or "Wishing Moon" (implying one could have a wish granted because of it's so-called rarity, like wishing on a falling star). I've tried to research it, but only found definitions.
Everyone is free to give any
Everyone is free to give any name to anything, and sometimes a definition sticks, sometimes it doesn't. There's rarely any logic behind it. Only two of the year's full moons are accepted by science and astronomers, the Harvest Moon around the September Equinox, and the next full moon after that, the Hunters Moon. No full moon consistently looks different from any of the others, though, let alone blue.
Thanks Bob. Love this artcle
Thanks Bob. Love this artcle especially cause I'm a moonchild
Thanks, I appreciate
Thanks, I appreciate that.....
"Slowly went viral"
"Slowly went viral"
i love what goes on in the
i love what goes on in the beautiful night sky
Thanks, Toni. We certainly
Thanks, Toni. We certainly have that in common.....
blue moons
Our first born was due the end of May 1988. He surprised us by being born the fifteenth. When all was settled down, we realized that he was born "in the middle of a blue moon." Not exactly correct but a conversation starter all the same.